Some Escherichia coli carry plasmids which confer on the host bacterium the ability: (1) to produce an antibiotic-like protein, called colicin whose adsorption to specific bacterial receptors leads to cell death, and (2) to survive treatment with homologous colicin, called immunity. To further our understanding of colicin action, we are undertaking a program (1) to study the events associated with mitomycin C induced synthesis of colicin I, (2) to isolate and characterize the E. coli colicin I specific receptor as well as to study its interaction with colicins, and (3) to correlate the structure of colicins with their biological specificities. To gain insight into the mechanism of drug induced colicin synthesis, we intend to investigate the effects of induction on Col I factor specific transcription. This will be accomplished by quantitating Col I-factor specific messenger RNA in non-induced and induced cells by (1) RNA hybridization to isolated Col I-factor DNA, and (2) isolation of colicin I specific mRNA in polysomes by immunochemical precipitation with anti-colicin I-gamma globulin. After characterization of the colicin I-receptor complex which we have isolated, we intend to purify the colicin I receptor and to examine its physical and chemical properties. We intend to probe the functional and topological organization of the bacterial cell-wall by genetic and biochemical characterization of colicin resistant mutants. We propose to investigate the effects of structural alterations of Colicin I (mutant and chemically modified molecules) on its biological properties (interaction with receptor, inability to kill immune cells, etc.). These studies will involve physical and chemical (primary structure) comparisons of wild type and altered colicin molecules.